This invention relates to separating the components of a gas stream. In one aspect, a high purity hydrogen stream is separated from a gas stream containing higher boiling components. In another aspect, the invention relates to an apparatus for separating the components of a gas stream.
Hydrogen containing streams are frequently encountered in plants in which feed stocks or other process streams are being hydrotreated or hydrogenated. Examples include hydroretorting of oil shale, hydrotreating heavy oils, hydroisomerization of hydrocarbons and hydrogenation of olefinic stocks. The hydrogen feed for such plants may be a byproduct stream such as from cat cracking gas oils or dehydrogenation of light hydrocarbons, so that the feed hydrogen may contain impurities such as carbon monoxide, light hydrocarbons, etc. Generally, the hydrotreating or hydrogenation process itself consumes only a fraction of the hydrogen feed. So there is substantial recycling of lower purity hydrogen to be handled within the process itself.
The usual practice in purifying hydrogen containing streams above the criconden bar is to reduce the pressure substantially to facilitate the condensation and removal of impurities after which the purified hydrogen must be recompressed. Due to the practical difficulties of compressing hydrogen and the unavoidable energy loss associated with decompressing and compressing the streams before and after the cryogenic purification scheme, a purification which avoids depressurization of the stream to be purified would clearly be highly desirable.